TW201410070A - Arrangement and method for driving light-emitting diodes - Google Patents

Abstract

The invention, which relates to an arrangement and a method for driving light-emitting diodes, is based on the object of specifying a solution for driving light- emitting diodes whereby improved driving of the LEDs is achieved without an impairment of the efficiency and/or of the harmonic content. The object is achieved in terms of a method by virtue of the fact that the second connections of all segments of the chain can be connected to a means for generating a constant current via a respective switching means, thus resulting in a number n of stages each comprising an n-th segment and an associated n-th switching means, that all switching means of all n stages are activated at an amplitude of the AC input voltage (VDC) of zero volts, that a comparison is made between an n-th reference voltage and a node voltage which can be measured at the second connection of a segment of the stage n+1, and that for the case where the n-th reference voltage becomes less than the associated node voltage, the switching means of the n-th stage is turned off.

Description

Device and method for controlling LED

The invention relates to a device for controlling an LED having an input capable of switching on an input voltage and having a series of LEDs connected in series with an output of the LED control device, the LEDs being divided into at least two segments, wherein each LED string Each segment has a terminal that is at least indirectly connected to a constant power source.

The invention also relates to a method for controlling an LED, by which a series of divided series of light emitting diodes can be prepared, wherein each segment comprises a plurality of light emitting diodes and has a first joint and a second joint, The LED string is operated using a rectified input alternating voltage (VDC).

The use of LEDs (light-emitting diodes) for lighting purposes is becoming more and more common, because LEDs have a number of advantages over traditional illuminators such as incandescent or fluorescent lamps, with lower energy consumption and use. Longer life is the biggest advantage. Since the LED has a current-voltage characteristic of the semiconductor, it is preferable to operate the LED at a constant current.

Therefore, when operating an illuminating device equipped with LEDs in a lighting network, appropriate circuit technical measures must be taken to generate the required low voltage for each LED from a very high alternating voltage (eg 230 VAC) from the power supply (usually Constant DC for 3 to 4V). The values mentioned above are generally applicable to so-called white LEDs, and if they are other LEDs, the values may vary.

In addition to the so-called AC-DC converters (usually composed of rectifiers and switching power supply components) that are widely used, one known method is to control a string via one or more linear power sources directly from the rectified alternating voltage. LEDs in series.

This device is also known as "direct AC LED". An advantageous way is to segment the LED strings and switch them on and off individually or one by one depending on the instantaneous alternating voltage. The number of LEDs in series and the forward voltage of the entire LED string are designed to meet most of the amplitude of the supply voltage, such as an amplitude range of 80% to 90% of the supply voltage.

Therefore, the voltage drop across the linear power supply can be kept to a low level, which helps achieve relatively high efficiency. When the instantaneous voltage is small, only a portion of the LED string is controlled by the associated power supply at a relatively low voltage drop in accordance with the segmentation at the device end. This will increase the current conduction angle during the half power cycle, resulting in a uniform light output. The current can be selectively adjusted based on the instantaneous supply voltage to increase the "power factor", that is, to keep the harmonic content of the supply current at a very low level.

Compared with the use of an AC-DC converter, this known method has the advantages of a small form factor and a low cost for controlling electronic components, and does not have a fast exchange edge, so the device's EMV (electromagnetic compatibility) ) is also better.

The main disadvantage of the high pulsation frequency of a light output with double power frequency is that sensitive people may feel disturbed. If the number of segments acting is less than the number of segments in the LED string, even if a constant supply of power to the LED, the light output will decrease.

If the instantaneous voltage of the control LED string is reduced to a level lower than the forward voltage of the first segment of the LED string, the current will become zero, that is, there will be a gap in which no power is supplied to the two LEDs during each power cycle. Unlike filaments of incandescent lamps, which have high heat resistance, the pulsation of the input power can be suppressed, and the light output of the LED is actually followed by the current change. In particular, the power gap may cause an uncomfortable feeling of illumination called "flash" or "flicker" (also known as "Flicker" in English).

Another control disadvantage is that the switching threshold of each segment must match the number of LEDs in each segment and the actual forward voltage.

It is an object of the present invention to provide an apparatus and method for controlling an LED that enables better control of the LED without degrading efficiency and/or harmonic content.

Furthermore, the switching threshold between the LED strings should be able to automatically adapt to the forward voltage of the segments of the LED string.

An advantage of the circuit arrangement having the features of claims 1 and 2 is the ability to provide uniform current to the LEDs within the string and to improve efficiency.

The method proposed by the present invention has the features of items 6 and 7 of the patent application scope.

The invention content of the main patent application can be further improved through the measures of the affiliated patent application.

Figures 1 and 2 show two possible embodiments of the prior art device 1 for controlling the LEDs 5. This is the so-called "direct AC LED" driver with 4 LED segments 6, namely LED-S1 to LED-S4. The LED string 4 is powered from the rectified supply voltage VCD2, wherein a constant current is generated by the ground terminal power supply 8 (ILED).

In the first figure, the segment 6 is short-circuited by the instantaneous voltages that are turned on via the LED string 4 by the switching elements SW1 to SW3 (for example, MOSFETs) as necessary.

In the embodiment of Fig. 2, the segment-branch point 7 is turned on to the common power source 8 (ILED) by the switching elements SW1 to SW3 in accordance with the instantaneous voltage turned on via the LED string 4. The task of the control unit CRL is to distribute the current to the individual segments 6 in conjunction with the instantaneous voltage. The power supply 8 (ILED) can be selectively adjusted according to the instantaneous power supply voltage VDC.

The manner in which the present invention automatically adapts the turn-on threshold to the forward voltage of the segment will be described below.

Figure 3 shows the principle of three segments (LED-S1 to LED-S3) of a LED string 4, each of which has any number of LEDs 5. The number of segments 6 can be arbitrarily increased, as shown by the dashed line at the joint 7 of the LED-S3 in the figure. Similarly, the number of LEDs 5 in each segment is freely selectable.

The anode of the "upper" LED 5 of segment 6 (LED-S1) is connected to the supply voltage VDC2 (i.e., the rectified supply voltage). Each segment 6 of the string 4 has a first joint and a second joint 7. In Figure 3, the first connector of the first segment 6 is connected to a voltage VDC. The second joint 7 of the first segment 6 is connected to the first joint of the next segment 6 of the string 4. Furthermore, this second joint 7 is connected to a switching element 9, 10, .

The entire LED string 6 is powered from a common ground terminal power supply 8 (ILED) via switchable elements 9, 10 that can be switched on and off. Above the power supply 8, there are provided so-called cathode-grid elements 9, 10 (TC1, TC29) for the opening elements for each current path n, for example of MOSEFT, bipolar transistors or IGBTs. The so-called cathode-grid refers to the series connection of two transistors, of which the "lower" transistor (in the n-channel or NPN) is responsible for control, and the "upper" transistor is responsible for increasing the breakdown strength and/or output impedance.

This will form n stages in the device, including the nth LED segment 6 and at least one nth switching element 9 or 10. The first phase includes the first segment 6 of the string 4 and the first switching element. It is also possible to include an element for controlling the first switching element 9. In the example of Figure 3, this component is a first comparator or amplifier 11 (AMP1).

The cathode-grid elements 9, 10 limit the voltage VQ on the power supply 8 and a portion of the voltage difference between the instantaneous voltage VDC and the forward voltage of the active segment 6 of the LED string 4. The maximum voltage VQ is determined by the gate voltage and/or the base voltage VGC connected to the ground-gate elements 9,10. For automatic threshold adaptation, it is preferred to keep this voltage low.

If the voltage VDC2 rises from a value less than the forward voltage of the segment 6 (LED-S1), the pilot current will first start when the forward voltage of the segment 6 (LED-S1) is reached. If the current limited by the power supply 8 is reached and the VQ reaches the value limited by the negative gate-ground gate element, the voltage VS1 of the commutator will also rise while the VC2 is further increased, while the VQ remains substantially unchanged. .

First, there will be no current passing through 6 (LED-S2), and the commutator inter-chip voltage VS2 is approximately equal to the voltage VQ. When the VDC reaches the sum of the forward voltages of segment 6 (LED-S1) and segment 6 (LED-S2), segment 6 (LED-S2) will also begin to pass current, while the current is distributed between TC1 9 and TC2 10 . The total current is still determined by the common power supply 8 (ILED). If VDC2 continues to rise, voltage VS2 will rise relative to VQ. This rise indicates that segment 6 (LED-S2) is electrically conductive while being able to cut off the current path via TC1 9. For example, the current path can be cut off via an amplifier or comparator 11 (AMP), wherein the comparison value of the amplifier or comparator 11 (AMP) is higher than the voltage VQ by a configurable comparison value. In order to avoid oscillations at the switching point, an advantageous way is to provide a comparator 11 with hysteresis. This applies in particular to the case of a high-ohm MOSFET as the cathode-grid element 9,10. If a bipolar transistor is used, its base current must be limited.

In order to avoid interfering radiation caused by the switching process, it is preferred to replace the comparator with a progressive disconnect generated by an amplifier with a moderate amplification or a simple inverter.

As shown in Fig. 4, it is also possible to receive current by TC2 10 without turning on TC1 9, wherein the control voltage VG2 > VG1 is turned on. When segment 6 (LED-S2) is conducting, TC2 10 will increase voltage VQ and TC1 9 will be automatically controlled. The voltage difference between VG2 14 and VG1 13 must be large enough to actually block TC1 9, which is especially important for integrating and applying fairly high ohmic MOFETs.

When the number of LED segments "n" is large, it may cause the control gate voltage VG1 to be "expanded" to VGn. It is therefore preferred to combine the phased control voltage with the open circuit of the previous current path.

If the LED string 4 is composed of more than two segments 6, the process described above will be repeated in the next phase or current path n+1, n+2... in the event that VOC2 continues to rise. The "last" segment 6 of string 4 does not necessarily require a cathode-grid component 9, 10, but for switching techniques, the voltage VQ is preferably limited. The latter cathode-grid elements 9, 10 are not necessarily connected. The example of Fig. 3 has two cathode-grid elements 9 and 10.

After VDC2 exceeds its amplitude and the voltage is again reduced, the cathode-grid elements 9, 10 are again activated by the same circuit in reverse order in accordance with the instantaneous voltage.

Fig. 5 shows an example of a voltage change curve in a half power supply cycle, taking the LED string 4 composed of four segments 6 containing the same number of LEDs 5 as an example. It can be seen from the figure that no LED 5 is operated and no LED current flows in the range where the alternating voltage 2 of the power supply terminal passes through the zero point. During a further time lapse of the positive half wave, the voltage VDC2 will rise until the forward voltage of the LED 5 of segment 6 (VLED-S1) is reached, and the current flows through segment 6 (VLED-S1), causing segment 6 (VLED- S1) Illumination. During the next half-wave process, voltage VDC2 continues to rise until the forward voltage of LED 5 of segment 6 (VLED-S1) and segment 6 (VLED-S2) is reached. From this point on, the current will also flow through segment 6 (VLED-S2), so segment 6 (VLED-S2) will also illuminate.

This process continues until all segments 6 (VLED-S1 through VLED-S4) are current flowing through and illuminate. After VDC2 reaches the maximum voltage, it will go down in a sinusoidal manner and will not reach the forward voltage of segment 6 (VLED-S4). This causes an interruption in the current in segment 6 (VLED-S4), which causes it to open. Segment 6 (LLED-S3), segment 6 (VLED-S2), and segment 6 (VLED-S1) will then be cut in sequence, so that no current will flow through string 4.

Embodiments having the same segment 6 facilitate the configuration on the application, but are not a prerequisite for the functionality of the method. For ease of understanding, the figure does not plot the voltage drop VQ above the power supply 8.

In Figures 3, 4 and 6, there is shown a constant power supply 8 with a control input through which a constant current can be controlled. It is therefore possible to selectively adapt the current change of the constant supply to the sinusoidal current change of the rectified ripple input voltage VDC using the input voltage VDC2. This adaptation improves the so-called power factor by reducing the interference harmonics.

In order to operate an LED lamp on a dimmer operating according to the phase cut-off method (Triac) or phase intercept method (MOSFET or IGBT), a current path must be provided for charging the power supply vessel, wherein the power supply voltage is within half a wave. The current conduction angle is determined by the capacitor.

When the forward voltage of the first LED segment 6 is reached and the timed capacitor can be charged, the aforementioned circuit 1 will begin to pass current. If no further action is taken, the maximum current conduction angle that the dimmer can achieve will become smaller. In order to avoid a small conduction angle of the current, it is advantageous to establish another current path which is already active when the supply voltage VDC is still lower than the forward voltage of the first segment 6 (for example LED-S1).

Since this current is not used to control the LED 5, it is called "leakage current". The circuit of Fig. 6 adds a cathode-gate element or switching element 16 (TCBL) and a comparator or amplifier 15 (AMPBL) to the circuit of Fig. 4 in accordance with the same principle. The "leakage current" will flow until the VDC exceeds the forward voltage of the further 6 (LED-S1). At this point the voltage VS1 will rise and the comparator 15 (AMPBL) will disable the "leak path". Power supply 8 (ILED) provides "leakage current" during the action of switching element 16 (TCBL).

It is also possible to reverse the polarity of the circuit layout described above, that is, the power supply 8 is connected to the positive supply voltage (VDC) while the cathode of the "lower" LED 5 is connected to the negative supply voltage (GND). Similarly, a high-end ("high side") power supply can be controlled with a ground or a potential-separated galvanometer.

1. . . LED control unit

2. . . Input

3. . . Output

4. . . LED string

5. . . led

6. . . segment

7. . . Interface/terminal

8. . . Constant power supply

9, 10. . . electronic switch

11,12. . . control unit

13, 14. . . The reference voltage

15. . . Comparator/Amplifier for "Leakage Current" AMPBL

16. . . Switching element TCBL

VDC. . . Input alternating voltage

GND. . . Cathode connection negative supply voltage

CRL. . . control unit

The present invention will be further described below in conjunction with the drawings and embodiments. Wherein: Figure 1: A possible implementation of a device of the prior art called a "direct AC LED driver" for controlling a light-emitting diode, Figure 2: A prior art known as a "direct AC LED driver" Another possible embodiment of a device for controlling a light-emitting diode, FIG. 3 is a circuit arrangement for controlling a light-emitting diode of the present invention, which can automatically adapt a current path to a forward voltage of an LED segment, FIG. Another device for controlling a light-emitting diode of the present invention can automatically adapt a current path to a phased gate voltage. Figure 5: The rectified power supply voltage and the commutator inter-chip voltage are in a half-power cycle. Voltage variation curve, Figure 6: A circuit arrangement that automatically controls the "leakage current".

1. . . LED control unit

2. . . Input

3. . . Output

4. . . LED string

5. . . led

6. . . segment

7. . . Interface/terminal

8. . . Constant power supply

9, 10. . . electronic switch

11,12. . . control unit

13, 14. . . The reference voltage

VDC. . . Input alternating voltage

GND. . . Cathode connection negative supply voltage

Claims (9)

A device for controlling a light-emitting diode, having an input capable of turning on an input voltage, and having a series of LEDs connected in series with an output of the LED control device, the LEDs being divided into at least two segments, wherein each LED string Each segment has a terminal connected at least indirectly to a constant power source, characterized in that: the first interface of the input terminal (VDC) is connected to the first interface of the first segment, and the second interface of the first segment is identical to the same string The first interface of the second segment is connected to the first interface of the first electronic switch having the control input, the second interface of the switch is connected to the first interface of the constant power source, the second interface of the constant power source is connected to a ground potential and an input terminal ( a second interface of the GND), the second interface of the second segment is connected to the first interface of the third segment, the first interface of the second electronic switch having the control input, and the first input of the first control unit, the switch The second interface is connected to the first interface of the constant power source, the second input end of the first control unit is connected to the first reference voltage, and the output end of the first control unit and the control switch of the first electronic switch The first input end of the second control unit is connected to the second interface of the third control unit, the second input end of the second control unit is connected to the second reference voltage, and the output end of the second control unit is connected to the second electronic The control input of the switch is connected. A device for controlling a light-emitting diode, having an input capable of turning on an input voltage, and having a series of LEDs connected in series with an output of the LED control device, the LEDs being divided into at least two segments, wherein each LED string Each segment has a terminal connected at least indirectly to a constant power source, characterized in that: the first interface of the input terminal (VDC) is connected to the first interface of the first segment, and the second interface of the first segment is identical to the same string The first interface of the second segment is connected to the first interface of the first electronic switch having the control input, the second interface of the switch is connected to the first interface of the constant power source, the second interface of the constant power source is connected to a ground potential and an input terminal ( The second interface of the GND) is connected, the second interface of the second segment is connected to the first interface of the second electronic switch having the control input, and the other interface is connected to the first interface of the constant power source, and the control of the first electronic switch The input terminal is connected to the first reference voltage, and the control input terminal of the second electronic switch is connected to the second reference voltage. A device as claimed in claim 1 or 2, characterized in that the first interface of the input terminal (GND) is connected to the control input of the constant power source. A device according to any one of claims 1 to 3, characterized in that the first and/or second control unit is an amplifier or comparator. A device according to any one of claims 1 to 4, characterized in that the first and/or second electronic switch is a MOSFET, a bipolar transistor, or an IGBT. A method for controlling a light-emitting diode, by which a series of divided light-emitting diodes can be prepared, wherein each segment can include a plurality of light-emitting diodes and have a first joint and a second joint, The LED string is operated by a rectified input alternating voltage (VDC), wherein the first interface of the first segment of the string is capable of switching on the input alternating voltage (VDC), and the second interface of all segments of the string is capable of Connected to a device that generates a constant current via a switching element, thus generating n stages, each having an nth segment and an associated nth switching element, when the amplitude of the input alternating voltage (VDC) is 0V, All the switching elements of the n stages are turned on, and the nth reference voltage and a node voltage are compared, wherein the second interface of the segment in the n+1th stage can measure the node voltage while When the nth reference voltage is less than the associated node voltage, the switching element of the nth stage is blocked. A method for controlling a light-emitting diode, by which a series of divided light-emitting diodes can be prepared, wherein each segment includes a plurality of light-emitting diodes and has a first joint and a second joint, and utilizes A rectified input alternating voltage (VDC) operating LED string is characterized in that: the first interface of the first segment of the string is capable of switching on the input alternating voltage (VDC), and the second interface of all segments of the string is capable of A switching element is coupled to the means for generating a constant current, thereby generating n stages having an nth stage and an associated nth switching element, respectively, when the amplitude of the input alternating voltage (VDC) is 0V, all n All the switching elements of the phase are turned on. When the amplitude of the nth node voltage exceeds the threshold value specified in each stage, the switching elements of the n-1th stage are blocked, wherein at the n+1th The second interface of one segment of the phase can measure the nth node voltage. A method according to claim 6 or 7, characterized in that the means for generating a constant current can be controlled by the amplitude of the input alternating voltage. The method of any one of claims 6 to 8, characterized in that a current path is prepared, and an adjustable current is generated in the current path without any current flowing through the string of the string. Minimum passing current.